Euro Force is a booster pack that needed to be fleshed out to be worth a purchase.
Battlefield 2: Euro Force is the first booster pack, the second being Armored Fury, which came out a few months later. Initially retailed for $10 online but can now be bought in stores if you don't want to jump on the "downloadable content" bandwagon; Euro Force adds in new things to Battlefield 2: Three new maps, a handful of new vehicles, and a new fourth faction: The European Union.
The European Union takes the place of the USMC in this booster pack, and like Battlefield 2, the maps face the EU against the Middle Eastern Coalition and the People's Liberation Army of China. The three maps themselves are based on relatively believable locales, such as a map that takes place on the Great Wall of China ("Great Wall", obviously), a map around a river nearby the Caspian Sea ("Taraba Quarry"), and a map involving retaining oil reserves in the middle east ("Operation Smoke Screen").
Since the European Union is a new faction, there are new weapons, some of which you can either unlock in Battlefield 2 or appear in other Battlefield 2 expansions such as Special Forces, new voices, and all that. The voices themselves sound a little flat and odd. I understand Europeans sound significantly different than Americans, but when the lines they speak sound very stilted and dull, it's hard to believe the speech they're saying is authentic. Other than new victory/defeat music for the EU, there is no other new sounds or music.
There's a bunch of new vehicles in the game, but a lot less than there really should be. There are new tanks like the Leopard 2A6 and Challenger 2, a new plane called the Typhoon T1, and the Tiger HAP helicopter. The rest are basically camouflaged versions of tanks and planes that the USMC use in Battlefield 2. At least it's nice to spruce up some old and put in some new, even if it looks very limited.
Euro Force is like its big brother in every way, since it's not really a modification, more of a map pack that you pay $10 for. Seriously, it's $15 more than you really should pay for. Since it's like a map pack, it plays in the main Battlefield 2 application, and still features some of the problems with that particular game, such as having a poor single player component, load times of up to 2-3 minutes (if you don't have a top-of-the-line computer), game slowdown and brief pauses.
Also, unlike the other maps in Battlefield 2, Euro Force has only 16-player and 32-player versions of the three maps. Since some of the servers for this booster pack hold more than 32 players, seeing 64 players on a map built for 32 is extremely hectic. Although this is not always the case, as some maps made for 32 and 64 players have little differences, so it's not that big a deal.
Euro Force is an expansion pack that should've been released either for free or for a very small fee (I'm thinking more in the range of $5 or less). Unless you are a Battlefield 2 completist, there is not much rhyme or reason to buy Euro Force.
Pros: New teams, vehicles and maps.
Cons: You're paying too much for very little, same game engine problems like Battlefield 2 (long load times, graphical chugging)